Romulan Type 4 was a material option, an Alpha Quadrant Alliance designation for the visual appearance of a spacecraft's outer hull, i.e. a vessel's "skin". Romulan Type 4 was available for some warbird classes of the Romulan Republic and its Romulan Republican Force. Type 4 put the ship in a cover of variously shaded greens. The warp plasma in the nacelles appeared bright green. (STO - "From the Ashes" mission: "Explore the Flotilla")
Related ship classes are sorted together, rather than alphabetically.